| With the continuous development and application of high density polyethylene(HDPE) in the field of life and industry, it is becoming more and more important to study the properties of HDPE geosynthetics. Although, the outdoor weathering test has a good simulation result for the materials, the aging time is longer and the non-controlling environmental factors influenced. That is why that the photo-oxidation aging property of materials is obtained by artificially accelerated aging test. However, with the difference of the emission spectrum of light source and the UV radiation intensity, the degradation degree of materials exists some differences. Therefore, it is necessary to study the properties of the HDPE geosynthetics, and analyze the effect of different UV radiation intensity on the photo-oxidation properties.In this paper, with HDPE geomembrane as the research object, the photo-oxidation aging was tested by using the method of artificially accelerated aging test under the effect of UVA340 and UVB313 two kinds of UV light sources. And macroscopic mechanical properties(breaking strength, elongation at break) of aging samples were tested, which shows the changes of the properties of the sample. At the same time, the aging samples were characterized by melt index(MI), crystallinity(DSC) and Fourier transform infrared spectroscopy(FTIR). At last, we explored the photo-oxidation aging degradation kinetics of HDPE geosynthetics, and analyzed the relationship of aging properties under different UV intensities.The specific research work as follows:(1) To explore the changes of photo-oxidation aging properties of HDPE geosynthetics in different intensities of UV radiation under the same source, UVA340 as a light source which was designed that there was one, two and four lamps were chosen. It was found that there is not a disproportionate between photo-oxidation aging reaction rate and UV radiation intensity, aging mechanism does not change at different intensities of UV radiation. The melt index analysis shows that with the increasing of radiation intensity, firstly the relative molecular mass increases and then decreases. But it is only about 10% in the increasing of crystallinity, which cannot fully explain the main reason of HDPE geomembrane material for aging degradation. FTIR shows that, double carbonyl absorption peak of ketone carbonyl and ester carbonyl were generated in the wavenumbers of 1712cm-1 and 1740cm-1, and the vinyl peaks in 908cm-1 wavenumbers, which accelerated the degradation reaction rate of HDPE material. The results showed that: under the same light sources, with the same cumulative UV radiation energy, the aging degree of the samples is inconsistent and the Reciprocity law does not apply to establish the aging correlation of HDPE geosynthetics. Therefore, we need to introduce constant p on the basis of Reciprocity law, namely Schwarzschild’s law, combined with the Arrhenius reaction rate function model to establish its aging correlation. It is found that when.p =770 at UVA340 light intensities, the photo-oxidation aging under different UV radiation intensities has a better correlation.The correlation equations of mechanical properties of aging samples between average UV radiation intensity and the aging time is:Breaking strength retention: t Iey77.000256.0100-=Elongation at break retention:-t Iy77.0=09.05.104Where, I is intensity of UV radiation intensity, W ? m-2; t is aging time, h.(2) To explore the differences of aging properties of aged samples under different light sources, UVA340(4 lamps) and UVB313(4 lamps) were chosen to analyze, and character the macro property, micro index. Melt index analysis showed that the degree of sample irradiated by UVA340 is far less than that by UVB313, but the aging mechanism of two UV lamps has not changed, which all generated double carbonyl absorption peak ketone carbonyl and ester carbonyl group is 1712cm-1 and 1740cm-1 at the wave number of the infrared spectrum. The results show that with the same cumulative UV radiation energy, the mechanical properties has significant differences when the sample was irradiated under UVA340 and UVB313 light sources, makes that it still cannot be applicable to Reciprocity law. Since the emission spectrum of the light source is different, and the existence of most sensitive wavelength for materials, there is the concept of effective UV radiation coefficient under different light sources. Calculated by UVA 340 and UVB 313 light spectrum, the effective radiation coefficient values α1 and α2 are respectively 0.56 and 0.84. It is showed that there is a good correlation when.p =062 under UVA340 and UVB313 lamps. Thus, the relationship equation between the index and average the intensity and the aging time under two different lamps is: Breaking strength retention: t Iy-06.2=06.01.103 Elongation at break retention: t Iey06.200284.0100×-= Where, I is intensity of UV radiation intensity, W ? m-2; t is aging time, h. α is the effective radiation coefficient.Based on the above conclusions, the aging mechanism of HDPE geosynthetics under different UV intensities has not changed, but its aging reaction rate is not consistent with the proportional changes of radiation intensity. Also, because of different emitting mechanism of two kinds UV light source, the concept of effective radiation coefficient is introduced to improve simulation results of outdoor atmospheric environment with artificial accelerated aging test, as a foundation for life prediction of HDPE geosynthetics under natural conditions. |
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